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Standard XII

Physics

Lens Formula

An image of t...

Question

An image of the sun is formed by a lens, of the focal length of 30 cm, on the metal surface of a photoelectric cell and a photoelectric current I is produced. The lens forming the image is then replaced by another of the same diameter but of focal length 15 cm. The photoelectric current in this case is :

\frac{I}{2}

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I

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2 I

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4 I

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Solution

The correct option is B $I$
Lenses of same diameter collect equal amount of light.
Intensity is measure of amount of light collected, hence the intensity remains the same.
Intensity is measured by the photoelectric current. So the photoelectric current would also remain the same.

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Similar questions

Q. An image of the sun is formed by a lens of focal length

30 c m

on the metal surface of a photoelectric cell and a photoelectric current I is produced. The lens forming the image is then replaced by another of the same diameter but of focal length

15 c m

. The photoelectric current in this case is:

Q. A lens of focal length

f

produces an image of an object located

15 c m

on one side of it at a distance of

30 c m

on the other side. If the lens is replaced by another lens of focal length

\frac{f}{2}

, where would the image form? If the image has to form at the earlier position by what distance should the object be shifted?

If an object is placed at 60 cm before lens I focal length of lens I is 30 cm and focal length of lens II is 45 cm., find out the image distance formed by lens II from O.

Q. A convex lens

L 1

forms an image of the same size as that of the object at a distance of

24 c m

. If the lens

L 1

is replaced by another convex lens

L 2

, the image formed is magnified and erect. Therefore, the focal length of

L 2

(a) A small object is placed 150 mm away from a diverging lens of focal length 100 mm. (i) Copy the figure below and draw rays to show how an image is formed by the lens. (ii) Calculate the distance of the image from the lens by using the lens formula. (b) The diverging lens in part (a) is replaced by a converging lens also of focal length 100 mm. The object remains in the same position and an image is formed by the converging lens. Compare two properties of this image with those of the image formed by the diverging lens in part (a).

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The correct option is B ILenses of same diameter collect equal amount of light.Intensity is measure of amount of light collected, hence the intensity remains the same.Intensity is measured by the photoelectric current. So the photoelectric current would also remain the same.

The correct option is B $I$
Lenses of same diameter collect equal amount of light.
Intensity is measure of amount of light collected, hence the intensity remains the same.
Intensity is measured by the photoelectric current. So the photoelectric current would also remain the same.